Electronic steering motors use current or voltage control to obtain the desired operating torque. In order to control voltage controlled surface magnet brushless motors, a voltage reference vector in polar coordinates is typically generated such that the efficiency is maximized until the magnitude of the voltage approaches the DC input voltage to the controller. After that, the phase angle is changed to obtain the desired torque with the limited voltage. Alternatively, surface magnet brushless motors can be current controlled using a current reference. Another type of brushless motor is an interior permanent magnet synchronous motor, also referred to as an interior magnet motor, which is typically controlled using current control relative to a current reference but may be controlled with voltage control relative to a voltage reference as well.